I. Field of the Invention
The present invention relates generally to antennas and, more specifically, to an increased bandwidth patch antenna.
II. Description of the Related Art
Antennas are an important component of wireless communication systems. Although antennas may seem to be available in numerous different shapes and sizes, they all operate according to the same basic principles of electromagnetics. An antenna is a structure associated with a region of transition between a guided wave and a free-space wave, or vice versa. As a general principle, a guided wave traveling along a transmission line which opens out will radiate as a free-space wave, also known as an electromagnetic wave.
In recent years, with the rise in use of personal communication devices, such as PCS phones, cellular phones and other communication devices, the need for small antennas that are suitable for use in personal communication devices has increased. An important factor to be considered in designing antennas for personal communication devices is the radiation pattern. In most applications, the communication device must be able to communicate in all directions. Therefore, the device must receive and transmit signals effectively in all directions. Consequently, in personal communication devices, it is essential that the antenna has an omnidirectional radiation pattern. Furthermore, the antenna must be compact in size in order to be suitable in a personal communication device.
One antenna commonly used in personal communication devices is the whip antenna. There are, however, several disadvantages associated with the whip antenna. Often, the whip antenna is subject to damage by catching on things. Even when the whip antenna is designed to be retractable in order to prevent such damage, it consumes scarce interior space. This results in less interior space being available for advanced features and circuits. Also, as personal communication devices such as cellular phones become smaller, the ability to use the whip antenna efficiently is being challenged.
Another antenna which may also be suitable for use in personal communication devices is the patch or microstrip antenna. The patch antenna was originally developed in the late 1960's for use with aircraft, missiles and other military applications requiring a thin or low-profile antenna. These applications required that the antenna neither disturb the aerodynamic flow nor protrude inwardly to disrupt the mechanical structure. The patch antenna satisfied these requirements.
The bandwidth of a patch antenna is proportional to the thickness of the dielectric substrate used. The thicker the substrate, the wider the antenna's bandwidth. In order to maintain desired bandwidth of personal communication devices, current patch antennas must have relatively thick substrates, which make them relatively bulky for personal communication devices. Since antennas in personal communication devices are required to be quite small in size, they would typically have thin substrates. Consequently, they would also have narrow bandwidth. Unfortunately, a narrow bandwidth restricts the utility of the antenna to a narrow frequency band. An increased bandwidth would allow personal communication devices to operate over a wider frequency band.